1. Field of the Invention
This invention relates to methods and compositions for preventing or treating diseases of a mammal, wherein at least one symptom of the disease is mediated at least in part by the binding of an effector molecule to a DC-SIGN receptor of the mammal to be treated. The effector molecule may be a molecule on a foreign organism. The foreign organism may be a virus.
The invention also relates to compositions, and to methods of identifying compositions, wherein the compositions are useful for treating mammalian diseases for which at least one symptom of the disease is mediated at least in part by the binding of an effector molecule to a DC-SIGN receptor of the mammal to be treated.
The invention further relates to compositions and methods for targeting subject molecules to cells expressing DC-SIGN receptors, such as dendritic cells. These compositions and methods are based on targeting complexes, in which one or more subject molecules are covalently attached to one or more DC-SIGN blockers and, by virtue of binding of one or more of the DC-SIGN blockers of the targeting complex to DC-SIGN, the subject molecule is targeted to cells expressing DC-SIGN receptors.
2. Description of the Related Art
Human Cytomegalovirus (CMV) is a double strand DNA virus belonging to the Herpesviridae family and a ubiquitous pathogen in humans. CMV interaction with its host is characterized by a primary infection followed by lifelong persistence in the host organism and viral reactivation episodes. CMV infection is asymptomatic in most immunocompetent individuals because of an efficient anti-viral immune response. In contrast, CMV remains a major cause of morbidity and mortality in newborn and immunocompromised patients, namely in organ-transplanted recipients or AIDS patients. In many cases, CMV disease is characterized by a wide viral spread toward multiple organs (i.e. salivary glands, lung, kidney, gastrointestinal tract, liver, retina, CNS).
In vitro, a number of cell types are susceptible to CMV infection when considering virus entry and viral immediate early gene expression. However, full replication of virus DNA and subsequent production of infectious virions is limited to permissive cells (i.e. fibroblasts, endothelial cells, the U373 MG astrocytoma cell line, etc.; see for review Plachter et al., 1996). In fibroblasts (the prototypic cell type for in vitro studies of CMV infection) CMV entry occurs in sequential steps involving several viral envelope (Env) glycoproteins. Initial attachment of virus to host cells is mediated through interaction between Env glycoproteins gB (CMV gB) and/or CMV gM with cell surface heparan sulfate proteoglycans (Compton et al., 1993; Kari and Gehrz, 1992). Thereafter, binding of CMV gB with non-heparin cellular receptors probably allows more stable attachment of virus to cell surface (Boyle and Compton, 1998). Subsequent pH-independent fusion events between viral envelope and cell membrane are necessary for viral entry (Compton et al., 1992; Milne et al., 1998). Cell proteins involved in CMV attachment and/or fusion have not been identified precisely although two candidates have been proposed. The first one is annexin II which interacts with CMV gB (Pietropaolo and Compton, 1997). The second one is a 92.5 kDa protein binding to CMV gH (Baldwin et al., 2000). Fusion events are followed by penetration of the capsid which is transported to the nucleus. In some permissive cells, such as retinal pigment epithelial cells, CMV can also penetrate into cells by a mechanism of endocytosis (Bodaghi et al., 1999).
Recently, dendritic cells (DC), which are refractory to infection by laboratory-adapted CMV strains, were shown to be permissive to CMV infection and replication when infected with primary, clinical viral isolates (Riegler et al., 2000).
Dendritic cells are a diverse population of morphologically similar cell types found in lymphoid or non-lymphoid tissues. Dendritic cells function as antigen-presenting cells that efficiently capture antigens in the peripheral tissues and process them to form MHC-peptide complexes. After antigen uptake, these immature dendritic cells acquire the unique capacity to migrate from the periphery to the T cell areas of the secondary lymphoid organs. Dendritic cells convert antigens from foreign cells and infectious microorganisms into short peptides that are bound to membrane proteins of the major histocompatibility complex (MHC). These MHC-peptide complexes are formed intracellularly, but are ultimately presented on the plasma membrane where they serve as ligands for antigen-specific T cell receptors (TCR). In addition to TCR ligand formation, dendritic cells carry out many other functions, which allow them to control immunity at several points (Steinman, 2000).
The mechanism of CMV entry into DC has not been investigated yet. It was recently shown that DC express a lectin called DC-SIGN (DC-Specific ICAM-Grabbing Nonintegrin). DC-SIGN, also called CD209, is a ligand for IntraCellular Adhesion Molecule-2 (ICAM-2) and ICAM-3 (Geijtenbeek et al., 2000a; Geijtenbeek et al., 2000c) and is involved in the attachment of Human Immunodeficiency Virus-1 (HIV-1) (Geijtenbeek et al., 2000b) and Ebola (Alvarez et al., 2002) to DC. DC-SIGN was originally cloned from a placental cDNA library on the basis of its capacity to bind to the surface subunit HIV-1 Env glycoprotein 120 (HIV-1 gp120) (Curtis et al., 1992). DC-SIGN mediates HIV binding and internalization into DC conferring to these cells the ability to transmit HIV to permissive CD4+ T cells independently from HIV-1 replication (Geijtenbeek et al., 2000b). These findings suggest that DC-SIGN efficiently captures HIV-1 at mucosal sites of inoculation and facilitates its transport to sites of infection by using the migratory ability of DC towards lymphoid organs (Banchereau and Steinman, 1998). A homologue of DC-SIGN, DC-SIGNR, was recently identified on the surface of endothelial cells and shown to display the same HIV-1 binding and trans-infection enhancement capacities shown by DC-SIGN (Bashirova et al., 2001; Pohlmann et al., 2001b). It has been suggested that the DC-SIGN lectin may act as a receptor for other glycan ligands present on other viral envelopes and on the cell walls of other microbes, or even tumor cells (Steinman, 2000). The putative role of DC-SIGN or DC-SIGNR in Herpesvirus attachment to DC or endothelial cells has never been reported.
There exists a need in the art to develop methods and compositions for modulating the specific binding of effector molecules to the DC-SIGN receptor, for example on the dendritic cells of mammals. Such methods and compositions are needed, for example, to prevent and treat diseases such as viral infections; for example CMV infections. In this regard, there is a need to identify cell proteins involved in viral attachment and/or fusion. Additionally, methods and compositions are needed that allow the specific targeting of cells expressing DC-SIGN receptor, such as dendritic cells or alveolar macrophages, to aid in therapy or diagnosis.